GEOLOGY. 253 



maiid in the market, for culinary purposes, and as a covering 

 for valuable buildings, instead of lead. But the chief con- 

 sumption of this metal is in making brass, well known to be 

 a compound of copper and zinc. In this process, the carbo- 

 nate of zinc, previously calcined, is mixed with charcoal and 

 granulated copper, and then exposed to a suitable heat. The 

 common brass imported from England contains upwards of 

 thirteen per cent, of zinc ; that of Paris, a little less ; and 

 the fine brass of Geneva, used in the nicer parts of watch- 

 making, contains as much as twenty-five per cent, of zinc. 



" Large quantities both of copper and zinc are now imported 

 from Europe into the United States, to supply the continually 

 increasing demand for brass. It is not improbable that the 

 district now under consideration might furnish of both metals 

 a sufficient amount, at least for many years to come, to sup- 

 ply the entire United States with brass of home produce and 

 manufacture. 



'* Of zinc, at least, there is assuredly a sufficient supply, 

 not only for that purpose, but also for exportation. All the 

 zinc now produced in Great Britain is trifling in quantity, 

 and quite insufficient for the demand ; so that a large quan- 

 tity is imported annually into that island, chiefl}^ from Ger- 

 many and Belgium. The importation of zinc into England, 

 in the year 1833, exceeded six millions and a half of pounds — 

 a fact which may give us an idea of the importance of this 

 metal as an article of commerce. 



Among the productive mineral resources of Iowa and 

 Wisconsin, the at present despised zinc ore may claim no 

 contemptible rank. 



IRON ORE. 



" The iron ore of this district is of excellent quality, and 

 in unlimited abundance. I explored, a few years since, in 



